- To compare detection of advanced neoplasia of CT colonography (CTC) to sigmoidoscopy (FS), a total of 20.000 eligible individuals living in the target areas are mailed an invitation letter to participate in the trial. All invitees are asked to call the screening centre in order to receive detailed information about study protocol, the screening examinations and the bowel preparation. Responders who consent to participate in the study are randomly assigned to undergo screening with CTC or FS. All non-responders will be invited to Fecal Occult Blood test (FOBT) according to the current screening procedure. In the CTC arm, positive patients (containing at least one polyp 6 mm or larger) are referred to colonoscopy; negative patients (no polyps >5 mm) are scheduled to be invited to have an FOBT after two years. In the FS arm, positive patients (at least one advanced adenoma found during FS examination) are referred to colonoscopy; negative patients are offered no further follow-up.